1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a semiconductor device capable of securing an adhesion film between an electrode and a semiconductor layer or a dielectric film in a electrode section of a semiconductor laser element.
2. Description of the Related Art
Recently, reduction in size and weight, and increase in reliability and power output have been advanced in the field of semiconductor devices, especially in semiconductor lasers, and such devices have been used as light sources in electronic equipment such as personal computers and DVDs, and in medical equipment. Among them, the group III-V Nitride semiconductors have been studied intensively because of their capability to emit light with relatively short wavelengths.
For example, as shown in FIG. 5, a semiconductor laser using a nitride semiconductor comprises an n-type semiconductor layer 32 of an n-type GaN layer and the like, an active layer 35 having an InGaN multiquantum well structure, and a p-type semiconductor layer 36 of a p-type AlGaN layer and the like, and having a ridge formed on the surface thereof that is stacked in sequence on a sapphire substrate 30 via an intermediate layer 31. An n-side ohmic electrode 33 and an n-side pad electrode 34 are stacked on the n-type semiconductor layer 32. The surface of the p-type semiconductor 36 is covered with an insulating layer 38 except the top surface of the ridge, and a p-side ohmic electrode 39 electrically connected to the p-type semiconductor layer 36 is disposed on the ridge. Further, the surface of the stacked structure comprising the p-side ohmic electrode 39, the n-type semiconductor layer 32, the active layer 35, and the p-type semiconductor layer 36 is covered with a protective film 37, except a portion of the p-side ohmic electrode 39. Then, a p-side pad electrode 40 electrically connected to the p-side ohmic electrode 39 is disposed on the protective film 37.
In such semiconductor lasers, reduction in drive voltage and improvement in luminous efficiency have been sought by lowering the resistance of the ohmic contact of the semiconductor layer and the electrode, which has been conducted by selecting a specific material for the electrode (for example, see Japanese laid-open patent application No. 5-291621, and Japanese laid-open patent application No. 6-275868), or by controlling the impurity concentration in the p-type semiconductor layer (for example, see Japanese laid-open patent application No. 10-303504).
However, even if an ohmic contact is established by using such various methods described above, the effect is not sufficient. Especially, when a semiconductor laser is mounted face-down, the semiconductor laser is connected to a heatsink, a stem, or the like, by way of die-bonding via a bump-electrode and the like. Therefore, heat generated in the course of die-bonding is transmitted directly to the bump electrode, the protective film 37, and the like, and adversely affects the performance of the semiconductor laser. That is, when the hot-melt material of for example the bump electrode (for example, Au—Sn eutectic) hardens, the residual stress arising from heat causes distortion. The distortion then concentrates on a portion having weak adhesion and causes a separation between the p-side pad electrode and the insulating layer and between the insulating layer and the p-side ohmic electrode and the like.
If at least one film such as the insulating film and the protective film is disposed between the semiconductor layer and the p-side ohmic electrode, the insufficient adhesion between such films and the materials of the electrode causes problems such as impairment of ohmic contact between the electrode and the semiconductor layer and detachment of the electrode from the semiconductor laser, in the manufacturing processes of the semiconductor device.